#pragma once

#include <ATen/cuda/ATenCUDAGeneral.h>
#include <ATen/cuda/CUDAContext.h>
#include <ATen/cuda/Exceptions.h>
#include <c10/core/impl/GPUTrace.h>
#include <c10/cuda/CUDAGuard.h>
#include <c10/cuda/CUDAStream.h>
#include <c10/util/Exception.h>

#include <cuda_runtime_api.h>

#include <cstdint>
#include <utility>

/*
* `cudaEventExternal` is a torch-specific flag that is used to
* indicate that the CUDAEvent will be used only for synchronization
* with work outside of the cuda graph, rather than creation of
* cross-stream dependencies within a cuda graph. Resources:
* https://docs.nvidia.com/cuda/archive/12.9.0/cuda-c-programming-guide/index.html#cross-stream-dependencies-and-events
* https://docs.nvidia.com/cuda/archive/12.9.0/cuda-runtime-api/group__CUDART__TYPES.html#group__CUDART__TYPES_1g3457b81d1d32c6a00f6132fbc2693d47
* https://docs.nvidia.com/cuda/archive/12.9.0/cuda-runtime-api/group__CUDART__TYPES.html#group__CUDART__TYPES_1g0c23426b7252eaa9cef695859991304e
*/
#define cudaEventExternal 0x08

namespace at::cuda {

/*
* CUDAEvents are movable not copyable wrappers around CUDA's events.
*
* CUDAEvents are constructed lazily when first recorded unless it is
* reconstructed from a cudaIpcEventHandle_t. The event has a device, and this
* device is acquired from the first recording stream. However, if reconstructed
* from a handle, the device should be explicitly specified; or if ipc_handle() is
* called before the event is ever recorded, it will use the current device.
* Later streams that record the event must match this device.
*/
struct TORCH_CUDA_CPP_API CUDAEvent {
  // Constructors
  // Default value for `flags` is specified below - it's cudaEventDisableTiming
  CUDAEvent() noexcept = default;
  CUDAEvent(unsigned int flags) noexcept : flags_{flags} {}

  CUDAEvent(
      DeviceIndex device_index, const cudaIpcEventHandle_t* handle) : device_index_(device_index) {
      CUDAGuard guard(device_index_);

      AT_CUDA_CHECK(cudaIpcOpenEventHandle(&event_, *handle));
      is_created_ = true;
  }

  // Note: event destruction done on creating device to avoid creating a
  // CUDA context on other devices.
  ~CUDAEvent() {
    try {
      if (is_created_) {
        CUDAGuard guard(device_index_);
        const c10::impl::PyInterpreter* interp = c10::impl::GPUTrace::get_trace();
        if (C10_UNLIKELY(interp)) {
          (*interp)->trace_gpu_event_deletion(at::kCUDA, reinterpret_cast<uintptr_t>(event_));
        }
        AT_CUDA_CHECK(cudaEventDestroy(event_));
      }
    } catch (...) { /* No throw */ }
  }

  CUDAEvent(const CUDAEvent&) = delete;
  CUDAEvent& operator=(const CUDAEvent&) = delete;

  CUDAEvent(CUDAEvent&& other) noexcept { moveHelper(std::move(other)); }
  CUDAEvent& operator=(CUDAEvent&& other) noexcept {
    if (this != &other) {
      moveHelper(std::move(other));
    }
    return *this;
  }

  operator cudaEvent_t() const { return event(); }

  // Less than operator (to allow use in sets)
  friend bool operator<(const CUDAEvent& left, const CUDAEvent& right) {
    return left.event_ < right.event_;
  }

  std::optional<at::Device> device() const {
    if (is_created_) {
      return at::Device(at::kCUDA, device_index_);
    } else {
      return {};
    }
  }

  bool isCreated() const { return is_created_; }
  DeviceIndex device_index() const {return device_index_;}
  cudaEvent_t event() const { return event_; }

  // Note: cudaEventQuery can be safely called from any device
  bool query() const {
    if (!is_created_) {
      return true;
    }

    cudaError_t err = cudaEventQuery(event_);
    if (err == cudaSuccess) {
      return true;
    } else if (err != cudaErrorNotReady) {
      C10_CUDA_CHECK(err);
    } else {
      // ignore and clear the error if not ready
      (void)cudaGetLastError();
    }

    return false;
  }

  void record() { record(getCurrentCUDAStream()); }

  void recordOnce(const CUDAStream& stream) {
    if (!was_recorded_) record(stream);
  }

  // Note: cudaEventRecord must be called on the same device as the event.
  void record(const CUDAStream& stream) {
    if (!is_created_) {
      createEvent(stream.device_index());
    }

    TORCH_CHECK(device_index_ == stream.device_index(), "Event device ", device_index_,
      " does not match recording stream's device ", stream.device_index(), ".");
    CUDAGuard guard(device_index_);

#ifndef USE_ROCM
    // it is an error to use cudaEventRecordExternal when not doing stream capture
    unsigned int flags = (c10::cuda::currentStreamCaptureStatusMayInitCtx() != c10::cuda::CaptureStatus::None && external_) ? cudaEventRecordExternal : cudaEventRecordDefault;
    AT_CUDA_CHECK(cudaEventRecordWithFlags(event_, stream, flags));
#else
    AT_CUDA_CHECK(cudaEventRecord(event_, stream));
#endif
    const c10::impl::PyInterpreter* interp = c10::impl::GPUTrace::get_trace();
    if (C10_UNLIKELY(interp)) {
      (*interp)->trace_gpu_event_record(at::kCUDA,
          reinterpret_cast<uintptr_t>(event_),
          reinterpret_cast<uintptr_t>(stream.stream())
      );
    }
    was_recorded_ = true;
  }

  // Note: cudaStreamWaitEvent must be called on the same device as the stream.
  // The event has no actual GPU resources associated with it.
  void block(const CUDAStream& stream) {
    if (is_created_) {
      CUDAGuard guard(stream.device_index());
#ifndef USE_ROCM
      // it is an error to use cudaEventWaitExternal when not doing stream capture
      unsigned int flags = (c10::cuda::currentStreamCaptureStatusMayInitCtx() != c10::cuda::CaptureStatus::None && external_) ? cudaEventWaitExternal : cudaEventWaitDefault;
      AT_CUDA_CHECK(cudaStreamWaitEvent(stream, event_, flags));
#else
      AT_CUDA_CHECK(cudaStreamWaitEvent(stream, event_));
#endif
      const c10::impl::PyInterpreter* interp = c10::impl::GPUTrace::get_trace();
      if (C10_UNLIKELY(interp)) {
        (*interp)->trace_gpu_event_wait(at::kCUDA,
            reinterpret_cast<uintptr_t>(event_),
            reinterpret_cast<uintptr_t>(stream.stream())
        );
      }
    }
  }

  // Note: cudaEventElapsedTime can be safely called from any device
  float elapsed_time(const CUDAEvent& other) const {
    TORCH_CHECK_VALUE(
        !(flags_ & cudaEventDisableTiming) && !(other.flags_ & cudaEventDisableTiming),
        "Both events must be created with argument 'enable_timing=True'.");
    TORCH_CHECK_VALUE(
        is_created_ && other.isCreated(),
        "Both events must be recorded before calculating elapsed time.");
    TORCH_CHECK(
        query() && other.query(),
        "Both events must be completed before calculating elapsed time.");

    float time_ms = 0;
    // We do not strictly have to set the device index to the same as our event,
    // but if we don't and the current device is not initialized, it will
    // create a new cuda context, which will consume a lot of memory.
    CUDAGuard guard(device_index_);
    // raise cudaErrorNotReady if either event is recorded but not yet completed
    AT_CUDA_CHECK(cudaEventElapsedTime(&time_ms, event_, other.event_));
    return time_ms;
  }

  // Note: cudaEventSynchronize can be safely called from any device
  void synchronize() const {
    if (is_created_) {
      const c10::impl::PyInterpreter* interp = c10::impl::GPUTrace::get_trace();
      if (C10_UNLIKELY(interp)) {
          (*interp)->trace_gpu_event_synchronization(at::kCUDA, reinterpret_cast<uintptr_t>(event_));
      }
      AT_CUDA_CHECK(cudaEventSynchronize(event_));
    }
  }

  // Note: cudaIpcGetEventHandle must be called on the same device as the event
  void ipc_handle(cudaIpcEventHandle_t * handle) {
      if (!is_created_) {
        // this CUDAEvent object was initially constructed from flags but event_
        // is not created yet.
        createEvent(getCurrentCUDAStream().device_index());
      }
      CUDAGuard guard(device_index_);
      AT_CUDA_CHECK(cudaIpcGetEventHandle(handle, event_));
  }

private:
  unsigned int flags_ = cudaEventDisableTiming;
  bool is_created_ = false;
  bool was_recorded_ = false;
  bool external_ = false;
  DeviceIndex device_index_ = -1;
  cudaEvent_t event_{};

  void createEvent(DeviceIndex device_index) {
    external_ = (flags_ & cudaEventExternal) != 0;
#ifdef USE_ROCM
    TORCH_CHECK(!external_, "External events are disallowed in rocm");
#endif
    flags_ &= ~cudaEventExternal;
    device_index_ = device_index;
    CUDAGuard guard(device_index_);
    AT_CUDA_CHECK(cudaEventCreateWithFlags(&event_, flags_));
    const c10::impl::PyInterpreter* interp = c10::impl::GPUTrace::get_trace();
    if (C10_UNLIKELY(interp)) {
      (*interp)->trace_gpu_event_creation(at::kCUDA, reinterpret_cast<uintptr_t>(event_));
    }
    is_created_ = true;
  }

  void moveHelper(CUDAEvent&& other) {
    // Transfer ownership of all state from other to this
    flags_ = other.flags_;
    is_created_ = other.is_created_;
    was_recorded_ = other.was_recorded_;
    external_ = other.external_;
    device_index_ = other.device_index_;
    event_ = other.event_;

    // Reset other to a valid empty state to prevent double-free
    // The moved-from object must not attempt to destroy the event
    other.is_created_ = false;
    other.event_ = cudaEvent_t{};
  }
};

// EventPool - Thread-safe pool of CUDA events to avoid expensive cudaEventCreate
// calls. cudaEventCreate when concurrently invoked from multiple threads can be
// very expensive (especially on certain device/driver combinations).
using CUDAEventPtr =
    std::unique_ptr<CUDAEvent, std::function<void(CUDAEvent*)>>;

class EventPool {
 public:
  EventPool() : pools_(at::cuda::device_count()) {}

  CUDAEventPtr get(const DeviceIndex device) {
    // If the device is invalid, return a default event and no pooling
    if (device < 0 || device >= (DeviceIndex)pools_.size()) {
      auto deleter = [](CUDAEvent* event) {
        delete event;
      };
      return CUDAEventPtr(
        std::make_unique<CUDAEvent>(cudaEventDisableTiming).release(), deleter);
    }

    auto& pool = pools_[device];

    // Create a destructor that returns the event to the appropriate device pool
    auto destructor = [&pool](CUDAEvent* event) noexcept {
      if (event != nullptr) {
        std::lock_guard<std::mutex> lock(pool.mutex_);
        pool.event_pool_.emplace_back(event);
      }
    };

    {
      std::lock_guard<std::mutex> lock(pool.mutex_);
      if (!pool.event_pool_.empty()) {
        auto event = std::move(pool.event_pool_.back());
        pool.event_pool_.pop_back();
        return CUDAEventPtr(event.release(), destructor);
      }
    }

    return CUDAEventPtr(
        std::make_unique<CUDAEvent>(cudaEventDisableTiming).release(),
        destructor);
  }

  void empty_cache() {
    for (auto& pool : pools_) {
      std::lock_guard<std::mutex> lock(pool.mutex_);
      pool.event_pool_.clear();
    }
  }

  void init_num_events(const size_t num_events) {
    for (DeviceIndex device_idx = 0; device_idx < at::cuda::device_count(); ++device_idx) {
        CUDAGuard device_guard(device_idx);
        std::vector<CUDAEventPtr> temp_events;
        temp_events.reserve(num_events);
        for (size_t i = 0; i < num_events; ++i) {
          auto event = get(device_idx);
          // Record the event to ensure it's properly initialized
          event->record();
          temp_events.emplace_back(std::move(event));
        }
        // Events will be returned to pool when temp_events is destroyed
    }
  }

 private:
  struct alignas(64) PerDevicePool {
    alignas(64) std::mutex mutex_;
    std::vector<std::unique_ptr<CUDAEvent>> event_pool_;
  };

  std::vector<PerDevicePool> pools_;
};

} // namespace at::cuda
